DE 37 21 398 A1 describes a delivery unit comprising a pump with a drive device, with the pump being surrounded on all sides by a pump housing which has a suction area with an induction opening, and a pressure area with an outlet opening. The pump housing is designed to be water-tight and is connected to a motor housing, which is likewise designed to be water-tight, holds the drive device and encloses a motor area which surrounds the encapsulated drive unit and is separated from the suction area in a liquid-tight manner. The motor area is filled with a barrier medium, in the present case with oil, which is used to lubricate the bearing, any gearwheels or the like, acts on the seals, and emits the heat via the motor housing to its surrounding area. Underwater delivery devices such as these are used to deliver hydrocarbons in the sea.
Resources are being discovered at ever greater water depths in the sea for crude oil and natural gas production, and water depths up to 4000 m are no rarity in this case. The requirements for pipeline systems and delivery units, relating to the capability to resist hydrostatic pressures from the outside resulting from the water pressure head and internally from the reservoir pressure caused by the crude oil and natural gas, are also correspondingly becoming more stringent. Normally, pipeline systems for deep-ocean delivery are designed for an overpressure from the inside of 300 to 500 bar, and must withstand an overpressure from the outside of up to 400 bar, depending on the water depth.
As additional requirements, the temperatures of the surrounding water and those of the delivery medium or process medium are different, and while the water temperature is between 1 and 4° C., the process medium will become hot up to more than 100° C., thus resulting in correspondingly high thermal loads. All components which are integrated in a delivery system must at least be able to withstand the loads mentioned above.
Pump systems for delivery of hydrocarbons in the deep ocean are generally designed such that the pump and the drive device, such as the motor and clutch, are installed in a common housing. This avoids the technically critical need to pass a shaft from the pump housing to the motor housing. In this case, there is an area which is filled by the process medium, specifically the suction area, the delivery chambers of the pump and the pressure area, and an area which is not filled by the process medium, with the motor, bearing and clutch. The two areas are separated from one another by shaft sealing; the area which is not filled with the process medium and has the motor, bearing and clutch area is filled with a barrier medium, normally with water or oil.
This concept has the disadvantage that there is a close link between the pressure-beating housing and the narrow tolerances which are required for operation, for rotating elements and sealing components. It must be possible to absorb deformations caused by the pressures which occur of +350 to −500 bar and temperature fluctuations from 1° C. to more than 100° C., at a number of points which react sensitively to shape and position changes, for example bearings, shaft seals and a motor gap. Large viscosity fluctuations also occur in the barrier medium, when this is in the form of oil. When not in a delivery phase, the motor and the pump cool down to the ambient temperature when stationary; during operation, they are heated by the temperature of the process medium and by friction to 60° C. to 80° C. The barrier oil viscosities, which vary because of this, from about 100 cSt in a cold system and to less than 2 cSt in a hot system, require special measures in the barrier oil system. The lubricating and load-bearing capability of the barrier oil must be maintained both in the cold state and in the hot state. Furthermore, in the cold state, large hydraulic friction losses must be overcome, for example in the motor.
The number of sealing points to the surrounding area in an underwater delivery unit must be minimized as far as possible, since sealing points represent a potential fault source and have a tendency to leak, and a small leakage can be identified only with major difficulty, while any leakage should be avoided, for environmental protection reasons.
The joint delivery of crude oil and natural gas means that liquids and gases are transported alongside one another. When delivering crude oil and natural gas, a so-called multiphase mixture is delivered, in which there is a high probability of only one phase being temporarily present, that is to say only liquids or only gaseous components will be delivered over considerable time periods. Furthermore, the composition of the multiphase mixture fluctuates over a wide range and over relatively long time periods, thus resulting in particularly stringent requirements for the pump technology in this case.